Air Pollution's Impact On Aquatic Life Explained

Air pollution has a detrimental impact on aquatic life, affecting both marine and freshwater ecosystems. Sulphur and nitrogen emissions, as well as ground-level ozone, can cause eutrophication, a process where excessive nutrients, particularly nitrogen, lead to algae blooms and deplete oxygen levels in water bodies. This, in turn, can result in the loss of aquatic life. Additionally, acid rain, caused by emissions of sulphur and nitrogen oxides, increases water acidity, affecting flora and fauna and disrupting essential ecosystem services. Heavy metals, such as aluminium, released into water bodies can be poisonous to fish and other wildlife. Furthermore, air pollution can indirectly harm aquatic life by affecting vegetation that helps filter and clean water systems.

Eutrophication

Causes of Eutrophication

Effects of Eutrophication

• Decreased biodiversity: Eutrophication favours the growth of simple plant life, such as algae, over more complex plant life, reducing biodiversity.
• Increased water toxicity: Some algae release neurotoxins and hepatotoxins, which can be harmful to plants, animals, and humans. These toxins can move up the food chain, leading to the death of many animals and posing risks to humans who consume contaminated fish or shellfish.
• Invasion of new species: Eutrophication can make a limiting nutrient abundant, leading to shifts in species composition. For example, an increase in nitrogen might allow competitive species to invade and outcompete original inhabitants.
• Depletion of dissolved oxygen: Excessive algae growth blocks sunlight, causing wide swings in dissolved oxygen levels in the water. When algae die, their decomposition by bacteria further consumes oxygen, creating hypoxic or anoxic "dead zones" where aquatic life cannot survive.
• Economic impacts: Eutrophication and harmful algal blooms increase water treatment costs, reduce commercial fishing and shellfish harvests, impact recreational fishing and tourism, and decrease property values.

Preventing and Reversing Eutrophication

To prevent and reverse eutrophication, it is essential to minimise nutrient pollution from sewage, agriculture, and other non-point sources. Introducing bacteria and algae-inhibiting organisms, such as shellfish and seaweed, can help reduce nitrogen pollution and control the growth of harmful algae. Additionally, nutrient removal technologies, such as biofiltration using living material to capture and degrade pollutants, can be employed.

Acidification

Acid rain affects the ability of ecosystems to provide "ecosystem services" such as nutrient cycling, carbon cycling, and water provision, which are essential for the planet and human life. Acid rain also impacts vegetation, which helps to naturally filter water systems and capture carbon, reducing the impacts of climate change.

Soils with higher concentrations of calcium carbonate, such as limestone and dolomite, are more resistant to acid rain due to the calcium carbonate's ability to chemically neutralize acids. This process is known as "liming" and is often used as an ecological restoration method to adjust the pH of lakes affected by acid rain. Soils that contain lower levels of calcium carbonate and are particularly vulnerable to acid rain include those found on quartzite, gneiss, and granite, as well as other metamorphic rock deposits such as those found throughout the Canadian Shield.

As soils become more acidic, their ability to retain essential nutrients, minerals, and elements decreases. This leads to a reduction in plant growth and water quality. Nutrients such as calcium, magnesium, and potassium are leached from the soil by water, making them less available for land organisms.

Increased soil acidity can also increase the mobilization of heavy metals within the soil, such as aluminum. These metals are then transported into lakes, rivers, and streams, where they can be poisonous to fish and other wildlife.

Water bodies can experience short-term but dramatic acidification, known as "acid shock," when acid precipitation in the form of snow is suddenly released into the water system during the spring melt. This can be lethal for many aquatic organisms. Alternatively, water bodies can become more acidic over the long term due to ongoing exposure to acid precipitation.

Lakes affected by acid precipitation are often clear because vegetation and aquatic wildlife cannot withstand lower pH levels. However, not all acidified water bodies are clear. Some aquatic ecosystems deficient in nitrogen may experience rapid and significant increases in plant and algal growth due to acid precipitation formed from the release of nitrogen oxides. This excessive growth, known as eutrophication, can eventually deplete the oxygen resources needed by other organisms in the lake or pond.

Heavy metal poisoning

Heavy metal pollution in water sources is a significant global concern, threatening aquatic ecosystems and human health. Heavy metals are toxic, potentially carcinogenic, and can bioaccumulate in biological systems. Sources of heavy metal pollution include mining waste, landfill leachates, municipal and industrial wastewater, urban runoff, and natural phenomena such as volcanic eruptions, weathering, and rock abrasion.

Heavy metals can cause harm to various organs, including the neurological system, liver, lungs, kidneys, stomach, skin, and reproductive systems, even at low exposure levels. Some heavy metals, such as hexavalent chromium, lead, and cadmium, are introduced into the environment through industrial processes such as tanning, electroplating, coal mining, agricultural activities, and the steel industry.

Heavy metal ions can enter the human body through the ingestion of contaminated food and water, skin contact, or inhalation of contaminated air. These ions can pass through cell membranes and interfere with cell organelles, leading to toxic effects.

Several technologies are available for minimizing heavy metal ions in water, including physiochemical methods such as filtration, ion exchange, and reverse osmosis. However, these methods have limitations, including the generation of secondary toxic sludge and high operational costs. As a result, there is a growing focus on developing cost-effective and eco-friendly methods for heavy metal removal, such as biosorption using biochar and natural zeolite ion exchangers, as well as advanced oxidation processes (AOPs) for the decomposition of heavy metal complexes.

Ozone damage

Ozone depletion increases the amount of UV-B radiation that reaches the Earth's surface. This has a range of effects on aquatic life, including:

• Damage to phytoplankton and zooplankton: Phytoplankton and zooplankton are the foundation of aquatic food webs. They are highly sensitive to UV-B radiation because they lack protective outer layers. Ozone depletion can reduce their populations, threatening the entire marine food chain.
• Damage to fish, shrimp, crab, and other marine animals: UV-B radiation has been found to cause damage to the early developmental stages of these animals, reducing their reproductive capacity and impairing their larval development.
• Effects on biogeochemical cycles: Increases in UV-B radiation could alter terrestrial and aquatic biogeochemical cycles, affecting sources and sinks of greenhouse gases and chemically important trace gases.
• Effects on materials: Synthetic polymers and naturally occurring biopolymers are adversely affected by UV-B radiation. Increases in UV-B levels will accelerate their breakdown.

Temperature changes

Causes of Thermal Pollution

Thermal pollution is caused by both human and natural factors. The primary human cause is the use of water for cooling industrial machinery and power plants. During this process, cold water is pulled in to cool down machinery, and the resulting warm water is released back into natural bodies of water. This is common in power plants using fossil fuels, such as coal or natural gas. Urbanization, deforestation, and certain agricultural practices also contribute to thermal pollution. Natural causes include geothermal vents, hot springs, and volcanic activity.

Effects of Thermal Pollution

The effects of thermal pollution on aquatic life are significant. Warmer water has a reduced oxygen-holding capacity compared to cooler water. This decrease in dissolved oxygen levels can be detrimental to aquatic life, causing stress and even death. Additionally, the injection of warm water into deeper bodies of water can prevent oxygen from dispersing to deeper levels, further endangering aquatic organisms.

The increase in water temperature can also lead to algae blooms, which pose a threat to aquatic plants and animals. The growth of algae is further facilitated by the increased metabolic rate of aquatic organisms in warmer water, as they consume more food. This can result in a disruption of the food chain and a decline in biodiversity as some species migrate to more suitable habitats.

Thermal pollution can also have reproductive effects on aquatic organisms, reducing fertility and causing birth defects or deformed eggs. Certain species may be more vulnerable to these temperature changes, and the overall population may decrease.

Mitigation Strategies

To mitigate thermal pollution, the implementation of artificial lakes, cooling ponds, and cooling towers has been suggested. Additionally, regulating and monitoring temperature discharge limits by governments and environmental agencies can help enforce compliance and reduce thermal pollution. Embracing renewable energy sources, such as wind and solar power, is another effective way to reduce thermal pollution as they do not produce heated wastewater.

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